Process for the preparation of age resistant asphalt compositions



Sept 15, 1959 R. L. GRIFFIN 2,904,494

PROCESS FOR THE PREPARATION OF AGE RESISTANT ASPHALT COMPOSITIONS FiledAug. 15, 1955 A E F 5 2o 7 80 l l l 4 /B |5 so"). m

u- 9 E 3 3 1' l0 40m '2 2 I 2 5 20m I v I I o 0.5 L0 L5 2.0 300 400 500600 nouns AT 225 F, LOWEST MOLECULAR WEIGHT 0F BLENDING STOCK Her I FIG11 LESS THAN 400 SHORT M MOL.WT., DISCARD RESIDUE suzuoms STOCK,ALL IOVER 400 MOL. wT. REDUCED ASPHALT, I LESS THAN Io PEN., ALL OVER 400MOLW'E RECONSTITUTED INVENTOR ASPHALT AGE RE RAYMOND L. s IFFIN BY m m QHIS AGENT United States Patent Ofiice 2,904,494 Patented Sept. 15,1959

PROCESS FOR THE PREPARATION OF AGE RESISTANT ASPHALT COR [POSITIONSRaymond L. Griffin, Oakland, Calif., assignor to Shell DevelopmentCompany, New York, N.Y., a corporation of Delaware Application August15, 1955, Serial No. 528,339

'5 Claims. (Cl. 208-233) This invention relates to a process for theimprovement of asphalt compositions. More particularly, it relates to aprocess for improving the aging characteristics of asphalts.

Asphalts normally comprise straight run asphalts, cracked asphalts, andblown asphalts prepared from either of these materials, either with orwithout the aid of oxidation catalysts. The term asphalt is generallydirected to residues obtained from the distillation of petroleum and mayvary from extremely soft materials to hard, brittle compositionsexhibiting a conchoidal fracture. They are used principally in thepreparation of pavings of various kinds, as well as in roofingmaterials, pipe coatings, enamels, and the like.

In many instances it is desirable to utilize products which remainstable insofar as their viscosity or consistency is concerned during thelife of the product. For example, in road compositions it is highlydesirable to maintain the same consistency of pavement commensurate withchanges in temperature encountered during its life. However, this idealstate is seldom if ever reached and many explanations for changes in theproperties of asphalt during its life or use have been advanced. Thesechanges have been attributed to oxidation, changes in gel structure withaging, sources of the asphalt, components naturally present in a givenpetroleum crude, temperature of application insofar as it afliects thestructure of the components, mechanical stress and vibration to whichthe composition is subjected, and numerous other influences.

It is a well-known fact that these changes inphysical propertiesseriously limit the use of asphalts for many purposes and also greatlyshorten the useful life of asphalts for such purposes as roofing or moreparticularly, in pavements such as roads, etc. The problem of aging isespecially evidenced by a hardening of the asphalt. The increase inconsistency, i.e. viscosity, of the asphalt leads to secondaryundesirable effects such as cracking or stiffening of the article withwhich or in which the asphalt is incorporated. In roads, for example,this can lead to disintegration of the road as the asphalt becomesharder and is subjected to the vibration and stress caused by traffic.The problem-becomes accentuated in the asphalts having relatively lowpenetrations and high viscosities. Likewise, the undesirable increase inviscosity is noted especially where the asphalt is subjected eitherto'high temperatures, or to oxidation influences, as Well as tocombinations of these environments. Thus, it will be seen that asphaltsnormally employed either for paving or roofing purposes are especiallysubject to this undesirable process of age hardening.

It is an object of the present invention to improve the' agingproperties of asphalt compositions. It is another object of thisinvention to produce asphalts showing relatively high stability withrespect to viscosity change during its useful life. It is aparticularobjectofthis invention to improve the aging characteristics ofasphalts heretofore regarded as being unstable with respect to aging.Other objects will become apparent from the description of theinvention.

Now, in accordance with the present invention, it has been found thatthe aging stability of asphalts may be strikingly improved, especiallyin asphalts containing more than about 5% by weight of components havingmolecular Weights of less than 400, by reduction of suchasphalts toasphaltic residues having penetrations of less than about 10 andthereafter mixing with said asphalt an asphaltic cutter stock in anamount sulficient to provide an asphalt composition of a desiredpenetration grade, said cutter stock containing substantially nocomponents having molecular weights less than about 400. The inventionmay be described in similar terms by stating that the asphaltic residueshould be reduced such as by distillation so as to contain no componentshaving molecular Weights less than about 400 and thereafter blending thereduced residue with the cutter stock defined hereinbeforc.

In the description hereinafter, certain terms are to be understood asfollows: Asphalt is regarded as the residue obtained by the eliminationof relatively lower boiling components of petroleum to obtain acomposition composed of comparatively non-volatile components,principally hydrocarbons, and substantially free from oxygenated bodieswith little or no crystallizable parafiins. The scope of the definitiongiven on page 56 of the Fourth Edition of Abraham Asphalts and AlliedSubstances is regarded as the definition to be accepted here.

The term cutter stock is understood for the presen purpose to meanrelatively non-volatile components, preferably derived by thedistillation of short residues and other residual oils. The cutterstocks so utilized are to be defined as having substantially nocomponents of molecular Weight below about 400, and preferablysubstantially no components having molecular weights lower than about450. The upper limit of the molecular'weight of components present inthe cutter stock is immaterial to the practice of the present invention,since the critical limitation placed upon the present invention is withrespect to the lowest permissible molecular weight components. Thecutter stock, therefore, may comprise even a whole asphalt as long asthe composition contains substantially no components having molecularweights less than about 400. Normally, however, the cutter stocks willcomprise components falling within the boiling point range of thosewhich will first distill, such as in vacuum, from a petroleum residueimmediately following the elimination of those having molecular weightsbelow about 400, that is, those having molecular Weights between about400 and about 800. Their preparationwill be described more fullyhereinafter.

The term penetration will be understood to refer to the consistency orhardness of semi-solid and solid asphalts as determined by the ASTMMethod D5-25. The penetration is expressed in terms of hundredths of acentimeter which a standard needle penetrates a sample of asphalt understandard conditions of load, time and temperature. Unless otherwisespecified, the penetration as discussed in the present specification isthat determined at 25 C. (77 F.) with a gram load and 5 seconds time.

Wherever reference is made to viscosity throughout the specification(unless otherwise specified) it will be understood that the viscosity isgiven in poises and that the determination was made by the micro methoddescribed in a paper presented before the Division of PetroleumChemistry of the American Chemical Society imined by means of amicroviscometer, the paper referred to.

generally, include those "tion operation and normally refined asphaltsas Well as pre'se'nt invention is especially applicable to crackedfasphalts, since these are notorious for their poor agingcharacteristics when utilized as known heretofore.

oxygen and, more normally, temperatures for a time sufiicient todecrease the peneat their New York meeting September 11-17, 1954, byLabout and Van Oort. In this method, samples in the order of 12-30milligrams are aged on glass plates in films only a few microns thickunder prescribed conditions The viscosity of the aged material is thendeteralso described in Of course, samples may be tested in themicroviscometer without previously having been aged.

Asphalts falling within the above definition of asphalts derived from astraight distillareferred to as steam cracked asphalts. The

However, the process applies both to cracked asphalts and to stralghtrun asphalts, as well as to blown products prepared from asphaltsderived by either process. The blown asphalts are regarded as asphaltswhich have been subjected to an oxidation process usually involving airat relatively elevated tration of the product and make it more suitablefor such purposes as used in roofing compositions, and the like. Theoxidation or blowing may take place without any modification but may beconducted in the presence of such catalysts as ferric chloride,phosphoric acid, phosphorus pentoxide, aluminum chloride, chlorine,Friedel-Crafts catalysts, and other well-known blowing catalysts.

The invention will be described with reference, in part, to theaccompanying drawing, wherein:

Fig. I shows the aging stability as measured by change in viscosity ofseveral asphalts containing blending stocks having minimum molecularweights below 400 and above 400, respectively;

Fig. II shows the eifect of varying molecular weights upon the agingstability of a Santa Maria asphalt at "two different aging temperatures;and

Fig. III is a schematic representation of a typical process illustrativeof the invention.

A surprising feature of the present invention is the entirely unexpecteddilference between the effect of blending stocks containing componentsof less than 400 molecular weight as compared to the aging effect ofblending stocks having components above 400 molecular weight minimum.This is clearly illustrated by the examples and the results shown in thedrawing. The precise reason for this striking difference in behavior hasnot been clearly ascertained. However, as Fig. 11 illustrates, it is notmerely a direct correlation between molecular weight and the temperatureof aging. -The sharp difference between blending stocks having minimummolecular weight components above and below 400 molecular weight,respectively, is as evident at a test temperature of 140 F. as it is ata test temperature of 225 F. Since the blending stocks were derived bymolecular distillation or vacuum distillation of short residues, itwould be expected that the individual com- 'ponents would be similar instructure and merely gradually change in molecular weight as theboilingpoint of the blending stock is elevated. Even if this is true, however,then it merely emphasizes the surprising feature referred to andillustrated so clearly in the drawing which shows the sharp rise in therate of aging when blending stock components have molecular weightsbelow 400.

The blending stocks are employed in amounts surficient to render thereduced asphalt suitable for use as paving gradeasphalts, coating gradeasphalts, roofing A asphalts, and the like. The reduced asphalts aremeant to be the asphalts referred to hereinbefore, obtainable,

for example, from shortresidues or long residues from which the lowerboiling components had been removed to an extent that the reducedasphaltic residue has a penetration of less than about 10 and containssubstantially no components of less than 400 molecular weight.

In blending such residues back to a penetration suitable for pavinggrade asphalt, it is normally found that between about 50% and about ofthe blending stock is required. For roofing grade asphalts, it isnormally necessary to utilize between about 40% and about 70% by weightof the final composition of the subject blending stocks. Paving gradeasphalts normally have penetrations between about 40 and about 250 at 77F. and softening points between about and F. as measured by the ASTMring and ball method. Roofing grade asphalts, on the other hand,normally have penetrations of between about 11 and 40 at 77 F. andsoftening points between about and 220 F. Paving grade asphalts havehigh ductilities, usually above about 100 at 77 F. as measured by theASTM method, while roofing grade asphalts have low ductilities in theorder of l-5 centimeters minimum at 77 F.

In carrying out the process of the present invention, the hard asphalts,referred to hereinbefore as reduced asphalts, may be prepared by anynumber of Well-known methods as long as substantially all of thecomponents present having molecular weights less than about 400 areremoved. This can be done by steam refining or vacuum distillation ofshort or long residues, care being taken toward the end of the reductionprocess that all of the lower molecular weight components, i.e. below400 molecular weight, are removed. Combinations of cracking and vacuumdistillation occurring either simultaneously or in steps subsequent toone another may be employed, either with or without steam distillation.In the use of vacuum distillation, it is normally found thattemperatures in the order of at least about 200 C. are necessary toremove substantially all of the components having molecular weightsbelow about 400 when the vacuum employed is between about 1.0 and about2.0 mm. Hg pressure, absolute.

When employing thermal cracking conditions, it is usually preferred tosubject the residue to cracking initially while removing the relativelyvolatile products so produced and thereafter subjecting the remainingresidue to a vacuum distillation for the further removal of moderatelyvolatile materials. The latter are then re-fractionated for the removalof components having molecular weights of less than about 400, afterwhich at least part of the residue from the refractionation (havingcomponents substantially all of which are of more than 400' molecularweight) is reblended with the reduced residue for the preparation ofpaving or coating grade asphalts of improved aging stability.

As will be seen by examination of the Figs. I and II, the incorporation'of blending stocks containing components of less than about 400molecular weight results. in asphalt compositions which age at a fargreater rate than those wherein the components of less than 400molecular weight are absent. The rate of viscosity change upon agingbreaks sharply atjust about 400 molecular weight, regardless "of thesource of the blending stock and regardless of the specific hard asphaltwith which the blending stock is used. Consequently, one aspect of thepresent invention comprises cross-blending, by which is meant theutilization of blending stocks containing components of over 400molecular weight only combined as described hereinbefore with hardasphalts of the same or of different origins, i.e. from the same ordifferent crudes, so

that advantage may be taken not only of the high aging combinedtherewith.

As pointed out hereinbefore, Fig. I illustrates the rate of aging ofasphalt compositions, some of which contain blending components of lessthan 400 molecular weight, and others of which contain components ofgreater than 400 molecular weight minimum. Curve A illustrates the agingrate of a cracked asphalt containing blending components having aminimum of 370 molecular weight. This cracked asphalt was derived from aGulf-Stettler crude subjected to an initial thermal cracking operation,followed by a vacuum distillation. In the course of the latter operationthe residue was reduced to an asphalt having Zero penetration andcontaining no components of less than 400 molecular weight. Thereafter,45% by weight of a blending stock having components of 370 molecularweight minimum was combined with the hard residue to obtain an asphalthaving a penetration of 84 and an initial viscosity of l.80 poises, asmeasured by the microviscometer referred to hereinbefore, the viscositybeing measured at 25 C. According to the data given in Fig. I, it willbe seen that this blend when aged in air at 225 F. had 4% times itsoriginal viscosity after 0.5 hour.

Curve C in Fig. I represents another composition based on the samereduced asphalt derived from Gulf- Stettler crude by the same crackingprocess. However, the minimum molecular weight of the blending stockcombined therewith was 427. An insignificant viscosity increase occurredwhen this particular blend was aged in air at 225 F. for 2 hours. Thissame curve also represents a third blend wherein the reduced asphalt wasthe same as that employed in the previous two samples but wherein theblending stock contained components of a minimum of 515 molecularweight. This blend also showed a remarkable resistance to viscosityincrease upon aging.

Curve B in Fig. I illustrates a second cracked asphalt composition, inthis case derived from Alberta Crude. As in the case of theGulf-Stettler samples, the Alberta short residue was subjected to acracking operation followed by a vacuum distillation to obtain a reducedasphalt residue having zero penetration of 77 F. This was blended withcomponents removed during the vacuum distillation, the minimum molecularweight of said components being 322. Curve B shows that this blendtripled in viscosity after aging for 0.5 hour in air at 225 F. Thisblend contained 59% by Weight of the blending stock and the lattercomprised components boiling between about 420 C. at 760 mm. and about455 C.+ at 760 mm. and having molecular weights between about 322 andabout 496. Seven percent of the composition had a molecular weight ofabout 322.

When this same reduced asphalt from Alberta crude was blended withblending stock components having a minimum molecular weight of 496, 63%by weight of the blending stock being employed, and the lattercontaining components boiling above 455 C. at 760 mm., the resultingasphalt composition was extremely stable, as shown by the substantiallack of viscosity change indicated by Curve C in Fig. I.

Fig. II represents the aging characteristics of a Santa Maria reducedstraight run asphalt combined with blending stocks of a variety ofminimum molecular weights, these blends being tested at twotemperatures. Curve E represents the results obtained by blending theasphalt (having a penetration of about 0-10 and containing no componentsof less than 400 molecular weight) with blending stock componentsobtained by the molecular distillation of Santa Maria short residue toobtain a blended composition of 85--l00 penetration at 77 F. Theseblends contained the following proportions of the specific blendingstocks listed as follows:

Molecular weight distribution, Santa Maria blends I Moleculardistillation,

bottoms Curve F of Fig. II shows that the blend containing components of350 molecular weight minimum aged extremely rapidly when thecompositions were heated in air for 2 hours at 225 F. However, theremaining two blends containing 400 and 510 minimum molecular weightblending components, respectively, showed substantially no change inviscosity under these test conditions.

Curve E in Fig. II represents the same blends, as well as someintermediate blends heated for four days at F. in air. The change inviscosity, while of lesser order, is just as striking as in the case ofsamples heated at the higher temperatures. Blends containing componentsof less than about 400 molecular weight aged extremely rapidly, theviscosity of the aged blends reaching up to 23 times that of theoriginal sample, as compared with 23 times viscosity increase forsamples wherein the blending components were greater than a minimum of400 molecular weight.

Fig. III represents a typical process by which the subject age-resistantasphalt compositions may be prepared. In the process as represented,short residue is subjected to a distillation process. It Will beunderstood that this may be accompanied or preceded by previoustreatments such as cracking and/or vacuum flashing. The distillation maybe at atmospheric pressure or reduced pressure. Preferably thedistillation is arranged so that cuts may be taken, thus separating asdesired those of lower boiling point and lower molecular weight fromthose of relatively higher molecular weight. Preferably the separationis such that those having molecular weights above 400 minimum aresegregated from the components containing molecules of less than 400molecular weight each. When the reduced asphalt so obtained has apenetration of less than about 10 and contains substantially nocomponents of less than 400 molecular weight, it is considered that thebase stock, ie. the reduced asphalt, is in proper condition forblending. For this blending purpose, at least a portion of thedistillation cuts having minimum molecular weights of at least about 400are blended with the reduced asphalt so as to reconstitute an asphaltcomposition having paving, coating or roofing characteristics. It willbe understood, as brought out hereinbefore, that the blending stockshaving molecular weights above about 400 minimum may be derived fromother sources than the asphalt from which the reduced asphalt base isprepared.

1 claim as my invention:

1. In the process of preparing asphalts having improved aging stability,the steps comprising distilling a petroleum residue containing more thanabout 5% by weight of fractions of less than 400 molecular weight untilthe distillation products finally contain no components of less than 400molecular weight, whereby a reduced residue having improved stability isformed, said reduced residue having a penetration less than about 10 at77 F., and thereafter blending therewith 40-90% based on the blendedcomposition of an asphaltic oil composed substantially ex- 7 clusivelyof components having molecular weights between, abou 40.0. and. a u

2. In the process of preparing asphalts having improved aging stability,the steps comprising distilling a petroleum residue containing more thanabout by weight of fractions of less than 400 molecular weight until thedistillation products finally contain no components of less than 400molecular weight, whereby a reduced residue having improved agingstability is formed, said reduced residue having a. penetration lessthan about at 77 F., and thereafter adding to said residue a cutterstock, substantially all the components of which have molecular weightsgreater than about 400 in an amount sufiicient to form an asphaltcomposition having paving grade characteristics.

3. In the process of preparing asphalts having improved aging stability,the steps comprising distilling a petroleum residue containing more thanabout 5% by Weight of fractions ofless than 400 molecular Weight untilthe distillation products finally contain no components of less than400' molecular weight, whereby a reduced residue having improvedstability is formed, said reduced residue having a penetrationless thanabout 10 minimum at 77 F., and thereafter adding to said residue acutter stock substantially all the components of which have molecularweights greater than about 400 in an amount sufficient to form anasphalt composition having roofing grade characteristics.

4; In the process of preparing asphalts having improved aging stability,the steps comprising first distilling a petroleum residue containingmore than about 5% by weight of fractions of less than 400 molecularWeight until the reduced residue so formed finally contains nocomponents of less than 400 molecular Weight, volatilizing from thedistillate obtained in said first step substantially all of thecomponents having molecular weights below a o 0, e i g a r du l; cu rstock. mpo ed es.- sentially only. of components having molecularweights above bo t 00,, n re ycl ng tl a t lport on o sai 5 cutterstock, to, the reduced residue.

10 asphaltic oil, having molecular weights between aboutAQi) and 800,said asphalt composition containing; substantial?- ly no componentshaving molecular weights less than about 400.

15 References Cited in the file; of thisv patent UNITED. STATES PATENTS;

345 ,399 Warren July, 13', 1886 688,073 Dow 2. Dec. 3, 1901 1,413,260Clark Apr. 18, 1922 1,993,532 Skowronski Mar. 5, 1935 2,028,922 RoseJan. 28, 1936 2,128,885 Poole Aug. 301938 2,223,776 Anderson Dec. 3,1940 2,276,155 Carr Mar. 10, 1942 2,297,455 Brautigam et a1 Sept. 29,1942 2,308,245 Ortynsky Ian. 12;,1943 2,343,789 Morris Mar. 7, 19442,687,989 Goodwin. Aug,,3'1, 195*4 2,698,280 Hersberger et al. Dec. 28,,1954 2,762,757 Bedell et al Sept. 11, 1956 QTHER, REFERENCES Abraham:Asphalts and Allied Substances, D. Van Nostrand Co., Inc, N.Y., 1945,5th ed., vol. 1, pages 5 22 and 523.

5. AN ASPHALT COMPOSITION COMPRISING A RESIDUAL ASPHALT HAVING APENETRATION AT 77* F. LESS THAN 10 AND A CUTTER STOCK COMPRISINGPETROLEUM HYDROCARBONS IN AN AMOUNT BETWEEN ABOUT 40 AND 9/%, SAIDCUTTER STOCK BEING AN ASPHALTIC OIL HAVING MOLECULAR WEIGHTS BETWEENABOUT 400 AND 800, SAID ASPHALT COMPOSITION CONTAINING SUBSTANTIALLY NOCOMPONENTS HAVING MOLECULAR WEIGHS LESS THAN ABOUT 400.